to fuse or not to fuse

[shadowdancer]

just put in a salt water wash down pump and attached to my 15 amp panel. Do i need a fuse in between the panel and the pump ?

[Lake-Effect]

Originally Posted by shadowdancer

just put in a salt water wash down pump and attached to my 15 amp panel. Do i need a fuse in between the panel and the pump ?

• Do the pump instructions ask for or recommend a fuse somewhere?
• How many amps does the washdown pump take?
• What gauge of wire is going from the panel to the pump?

[skipmac]

Is the panel switch on/off only or is it a circuit breaker/switch? If the panel has a circuit breaker (the one on my Pearson 422 has circuit breakers) AND the entire wire run from the panel to the pump can easily and safely handle 15 amps without overheating or melting then you could go without the fuse. But putting a fuse inline to the pump can't hurt.

Forget who it was but some marine electrical guy who did presentations at boat shows and such used to do an interesting demonstration. At the start of the talk he would hook a bilge pump through an unfused wire to a battery, jam something into the pump rotor as might happen if your pump picked up some debris in the bilge and toss the pump into a bucket. Then start his talk. A couple of minutes later the wire to the pump starting smoking and melting and I think occasionally even catch fire.

[CharlieJ]

Further to @skipmac #3:
The demo he referred to exhibits the effect of a locked rotor condition.

The fine point is that manufacturers of marine pumps are required to provide their recommendation for over current protection to protect against a locked rotor event. The demo I am more familiar with included putting a 5A fuse in the B+ supplying the pump where the manufacturer would call for a 3.5A fuse. The AWG 16 pigtails could easily handle the 5A so no big deal. The pump would start to destructively overheat and the 5A fuse would not open.

So the advice is to install the size and type of OCPD that the pump manufacturer specifies. If I cannot match the OCPD requirement to a OTS circuit breaker, I usually install the fuse holder on the load side of the circuit breaker controlling the pump right at the breaker. This is to ensure that the fuse holder is not buried and forgotten.

[flightlead404]

Originally Posted by skipmac

But putting a fuse inline to the pump can't hurt.

I beg to differ.

Properly size the circuit interrupting device at the buss (fuse, breaker) based on the gauge of the wire.

Properly size the gauge of the wire run based on device current draw and the voltage drop over the run, and whether its in a bundle or free air.

Don't add additional failure points in the line.

[skipmac]

Originally Posted by flightlead404

I beg to differ.

Properly size the circuit interrupting device at the buss (fuse, breaker) based on the gauge of the wire.

Properly size the gauge of the wire run based on device current draw and the voltage drop over the run, and whether its in a bundle or free air.

Don't add additional failure points in the line.

I don't disagree with the idea of minimizing failure points in general but specifically, I cannot remember the last time I had a failure in a fuse that was not due to an overcurrent event. In 40 years of messing about in boating, car maintenance and general electrical and electronics stuff maybe once or twice has this happened. That includes corrosion or loose connections that resulted in an open circuit as well as blown fuses.

Yes proper sizing of wires with the circuit breaker is good and adds to safety.
However, considering the down side of an overheated wire and potential for fire the tradeoff of a very small risk of fuse failure vs the small risk of a catastrophic fire onboard I'll go with an extra fuse.

Another issue, most bilge pumps and indeed almost all electrical and electronic stuff I have on board has relatively small wires built into the device, wires that cannot be changed and small enough that a 15 amp breaker isn't going to protect that section of wire.

[skipmac]

Originally Posted by CharlieJ

Further to @skipmac #3:
The demo he referred to exhibits the effect of a locked rotor condition.

The fine point is that manufacturers of marine pumps are required to provide their recommendation for over current protection to protect against a locked rotor event. The demo I am more familiar with included putting a 5A fuse in the B+ supplying the pump where the manufacturer would call for a 3.5A fuse. The AWG 16 pigtails could easily handle the 5A so no big deal. The pump would start to destructively overheat and the 5A fuse would not open.

So the advice is to install the size and type of OCPD that the pump manufacturer specifies. If I cannot match the OCPD requirement to a OTS circuit breaker, I usually install the fuse holder on the load side of the circuit breaker controlling the pump right at the breaker. This is to ensure that the fuse holder is not buried and forgotten.

Could have been the same demo. It has been a while and some of the specifics of the talk could be a bit fuzzy in my memory.

[thinwater]

Originally Posted by skipmac

... I cannot remember the last time I had a failure in a fuse that was not due to an overcurrent event....

I agree with fusing. Eliminating failure points is not a reason to omit them. But...


Yes, I have experienced a number of fuses that have failed due to either external or internal corrosion in either marine or industrial applications. It's not that rare with Buss-type fuses. The challenge is very damp locations.

[skipmac]

Originally Posted by thinwater

I agree with fusing. Eliminating failure points is not a reason to omit them. But...


Yes, I have experienced a number of fuses that have failed due to either external or internal corrosion in either marine or industrial applications. It's not that rare with Buss-type fuses. The challenge is very damp locations.

Agreed. The few failures I recall were mostly due to corrosion. However I'm slightly smarter than I was when I first started boating and have learned that there are various goops one can apply to electrical thingies that prevent corrosion and improve conductance.

AND you can get Bus fuse holders that are two piece, push together, waterproof, rubber that are relatively waterproof.

[Boatyarddog]

The panel breaker/ fuse is adequate.
SV Cloud Duster

[flightlead404]

Originally Posted by skipmac

I don't disagree with the idea of minimizing failure points in general but specifically, I cannot remember the last time I had a failure in a fuse that was not due to an overcurrent event. In 40 years of messing about in boating, car maintenance and general electrical and electronics stuff maybe once or twice has this happened. That includes corrosion or loose connections that resulted in an open circuit as well as blown fuses.

Yes proper sizing of wires with the circuit breaker is good and adds to safety.
However, considering the down side of an overheated wire and potential for fire the tradeoff of a very small risk of fuse failure vs the small risk of a catastrophic fire onboard I'll go with an extra fuse.

Another issue, most bilge pumps and indeed almost all electrical and electronic stuff I have on board has relatively small wires built into the device, wires that cannot be changed and small enough that a 15 amp breaker isn't going to protect that section of wire.

Sure the fuse itself doesn't fail.

But the mechanical or solder connections to the fuse holder do. Esp since adding one usually means an in-line type of device which imho tend to be poor quality and often also unsupported, which adds vibration and weakens connections, especially soldered joints. Add on corrosion from a marine environment and some time....

I've seen all sorts of nightmares on electrical systems, wrong types of circuit interrupting devices, connections with sticky tape, speaker wire, the worst kind of soldering you can imagine, high gauge number wire wrapped around large cables, solid wire used where stranded s/b used, the list is endless. How some of these people didn't incinerate themselves I don't know

I guess when it comes to this sort of thing I'm in the camp of "just design it right and implement it correctly from the get go rather than band-aiding things"

[CarlF]

It's a good point that many pieces of marine equipment have smaller gauge wires inside that you can't see. Just fusing to the gauge of the supply wires leaves you open to a a fire in the piece of equipment.

Of course, a responsible manufacturer would internally fuse - or at least provide a sticker on the unit specifying the fuse size. But that's not the world we live in.

[Thumbs Up]

I think that you want the largest (fused from the panel) wire size that you can manage (within reason) going to the vicinity of the pump (to avoid voltage drop) then fuse it again at the pump lead according to the pump mfg. specs. (so that if you get a locked rotor, the pump won't melt while continuing to drain your battery). I use a 5 amp automotive spade type fuse in a capped holder. I can think of an improvement (untested by me): The secondary fuse could be a thermal circuit breaker of the type that resets itself after a few minutes. This way, instead of just blowing a fuse, the pump will make some last ditch efforts to restart itself after a few minutes. I can think of a few more improvements to the scenario as well such as a manual over ride switch so that you can quickly get it running again after you clear a blockage. And an alarm that tells you that the pump is blocked.

[Squanderbucks]

My preference is to never use a circuit breaker switch as the On/Off switch for a device.
Devices that can be directly powered from the panel might include nav equipment that each have their own internal switch on the front of the device.
If needed sub panels are used as well closer to the devices being serviced. Also circuit breakers are mostly higher AMP protectors down to about 5 AMPS. Many devices need 1. 2, 3, 5, 7.5 AMP protection.
I prefer to mount Blade type ATO sub panels for every small device. I do not like inline fuses as then you have fuses alll over the place instead of central places to look some fuse holders have red LED lights to show blown fuses. Very handy in dark places.

[skipmac]

Originally Posted by flightlead404

Sure the fuse itself doesn't fail.

But the mechanical or solder connections to the fuse holder do. Esp since adding one usually means an in-line type of device which imho tend to be poor quality and often also unsupported, which adds vibration and weakens connections, especially soldered joints. Add on corrosion from a marine environment and some time....

I've seen all sorts of nightmares on electrical systems, wrong types of circuit interrupting devices, connections with sticky tape, speaker wire, the worst kind of soldering you can imagine, high gauge number wire wrapped around large cables, solid wire used where stranded s/b used, the list is endless. How some of these people didn't incinerate themselves I don't know

I guess when it comes to this sort of thing I'm in the camp of "just design it right and implement it correctly from the get go rather than band-aiding things"

All valid points and when I bought my current boat found all of the above transgressions and more

. However all easily remedied by using the right parts and installing them correctly and in fact, adding a secondary safety factor IE an inline fuse, is even more important if there's a risk that the PO left some kind of bollixed up repair or installation in some hidden location in the circuit.

For inline fuses, high quality, reliable holders of various types are readily available and inexpensive. As another post mentioned, in many devices, including bilge pumps there are small lead wires AND the potential for internal shorts and fire.

It's hard to guard against stupid stuff foisted upon you by a PO so extra precautions are a good thing.

Also, for something like a small, dewatering bilge pump that might demand a 3.5 amp circuit protection I'm not sure you can find a 3.5 amp circuit breaker for a panel.